If you are in between two sizes of bikes, is it better to go with the larger or smaller one?

Larger would be my pick.

I had a touring bike that was one size too small.

Rode it 14,000 miles. made many adjustments.

Never got it to fit just right.

Depends on your riding style, flexibility, etc.

I'm between a 52 and a 54, somehow, and am much happier on my 52 Domane than I was on my 54 Defy. (And When I was bike shopping, the 52 Domane was immediately more comfortable than the 54 Domane. So it wasn't just a matter of the different geometries.)

Personally, I would go for smaller size. Easier to adust up than down.

I am like Wheever, between a 52 and 54 frame. To determine the size I fit myself to the top tube of the bike, much like is recommended by Sheldon Brown (Revisionist Theory of Bicycle Sizing). I brought a plumb line (string with washers) with me so I could roughly set the fore-aft at the correct position (roughly KOPS) and when on the hoods determined which size had my face over the fork tube/stem. Then I determined which frame felt too large. It turns out the 54 was too large due to handlebar reach as it would require a short stem (under 80mm) to not overreach to the handlebars. Keep in mind I have a short torso and long legs for my size.

Why do you think it's easier to adjust up than down?

Because, for one, lengthening your position via a longer stem has less of an impact on stable handling than going with a shorter stem. (For instance, my 52 Domane came with a 90mm stem. Going up to 100mm is almost unnoticeable in terms of handling changes; going down to an 80mm stem on my 54 Defy made handling twitchy, especially in the drops at high speed. Not dangerously so, but not the most comfortable feeling.)

Point being, you can raise the saddle, get a longer offset seatpost, and a longer stem if a bike is a little too small; if it's a little too big, you can go with a zero-offset post, sure, but the stem changes start to impact handling, and bringing the seat too far forward can place your knee in the wrong place over the pedal.

Like [MENTION=355467]Doc V[/MENTION], I have long legs and a shorter torso for my size, and though I have long arms, they're not long enough to compensate for my short torso when it comes to reach.

My first bike was a 56cm. Loved the bike, hated standing over it at stops. I would just stand on one leg straightened toward the floor, the other on the pedal.

Then got a 54cm. Much much better. Now I can stand over the bike with both legs on the floor. I can even sit on the top tube a lot easier. I love it.

Go smaller imo. You have much more options for adjustment.

I usually go smaller. My ideal TT is 55cm but most manufacturers will offer a 54 and a 56. I'd much rather use a 110 or 120mm stem on a 54 than a 90mm on a 56.

Another consideration is headtube height. The bigger frame will likely have a taller headtube and it may be difficult to get the stem low enough if you prefer a more agressive position.

Longer legs, shorter torso go smaller frame.
Shorter legs, longer torso go with larger frame.

Thanks. I'm the former. I tend to go for smaller for the shorter top tube, but sometimes I have to raise the seatpost so high that it's over the limit mark. But if I go with the larger frame, the stretching to reach the handlebar is very uncomfortable, esp. for long rides. I saw someone the other day so stretched out it's like crawling on all fours

A longer seat post is neither the hardest to find, nor the most expensive thing in the world.

As I said, go smaller. It's easier to make fit.

That's first time I've heard that articulated thus. Makes perfect sense.

Kind of like the Ape Index. I could swing from the trees so I always go larger ;-**

Looks like being standard or compact frame would effect the feel of the bike, even if the effective dimensions are the same. My MTB is a standard frame 23" and feels huge compared to my compact framed 60CM road bike. Although I required a shorter stem and less set back on my seatpost on the 60CM road bike the toptube being so low when I'm standing to pull a hill makes it feel......well, compact.

I've always preferred to go larger. I'm 6'2" and can sit either a 56 or 58 road bike frame but have found the 58 more adaptable. Perhaps if I was racer I'd find the shorter frame better.

Maybe that could translate into: Go with your torso, if it's relatively too long or too short.